1. Field of the Invention
This invention relates to load carrying cords as used as a component of a power transmission belt. The invention also relates to a power transmission belt incorporating the load carrying cord.
2. Background Art
A conventional power transmission belt has a body with a tension section and a compression section, with their being a neutral axis defined between the tension and compression sections by load carrying cords extending lengthwise of the body. Commonly, a cushion rubber layer is provided within which the load carrying cords are embedded. In one known construction, a V-ribbed belt is formed by embedding load carrying cords in a cushion rubber layer to which a cover canvas layer may be laminated. Multiple ribs are formed in the compression section. This type of belt is commonly used in the automotive environment, as an alternative to a V-belt, to drive components such as air conditioners, alternators, etc.
Typically, the load carrying cords in this type of V-belt/V-ribbed belt are made from polyethylene terephthalate (PET) fibers. PET fibers show better balance in terms of tenacity, modulus of elasticity, fatigue resistance, etc., than other fibers.
In the event that the heat shrinking stress of a belt is increased to avoid reduction in tension of the belt in operation, the dimensional stability of the belt may be reduced significantly over time.
To improve the dimensional stability over time, JP-A-50-16739 discloses a rubber reinforcing material, having good heat resistance and good dimensional stability, using polyethylene-2-6-naphthalate (PEN) fibers. However, bending fatigue is generally poorer with this type of fibers than with PET fibers.
JP-A-5-312237 discloses making the filament angle of the load carrying cords, made up of PEN fibers, from 15.degree. to 25.degree. to improve bending resistance. In JP-A-7-127690, a method of mixing and twisting PET filaments and PEN filaments is disclosed. However, with these cords, there is a problem that the modulus is lowered, a problem which is associated with load carrying cords using PEN fibers.